[Ninja_Bait]

The gearboxes have a long lead time on them, and they are also prone to breakage - the gears strip before the motor reaches stall torque, they're shipped with screws that are barely long enough to hold the thing together, and any little bit of grit will jam them up.

We used the 550 gearboxes on an arm and it was a nightmare. The mounting holes on the sides were poorly tapped and they were very difficult to repair. We now have more 550 gearboxes than we'll ever need, because we bought so many spares. (Though, now as I rant, I realize this information may not apply to the 775 gearboxes - the quality may differ between series...)

775's only have a free speed of ~7000 rpm anyway. You'd be better off doing a one-stage spur gear reduction similar to the guts of a CIMple, because you don't need too much of a reduction for a turret. We're doing something similar, also using two 775's and found that a 3 to 1 ratio was sufficient.